2-fluoro-1, 3-diene polymers



Patented Aug. 1948 amass z-r'wono-nz-nmmi POLYMERS Walter E. Mochel,Wilmington, Deli, assignonto E. I. du Pont de Nemours & Company,Wilmington, DeL, a corporation of Delaware No 1mm. Application May 20,1944,

Serial No. 536,613

2 Claims. (01. 260-92113 1 This invention relates to new, improvedrubher-like polymers and the process for preparing the same. Moreparticularly, it relates to improved polymers of fluoroprene(2-fluoro-1,3- butadiene).

In the manufacture of synthetic rubbers by polymerization of conjugateddlenes, it is standard practice to include with the polymeriza'blemonomers small proportions of certain modifying agents in order toobtain products which are sufficiently plastic to permit satisfactoryprocessing with conventional rubber equipment. Sulfur or sulfurcontaining compounds, normally employed with butadiene or chloroprenefor this purpose, are also effective as fluoroprene polymer modifiers,but with the latter diene in particular there is a' need for developingmethods by which still further improvements in plasticity and millbehavior of the products can be realized.

It is therefore the object of the present invention to providerubber-like fluoroprene polymers and copolymers of improved plasticityand better processing characteristics. A further object is to provide amore economical process for preparing synthetic rubbers based onfluoroprene.

These objects have been accomplished by the polymerization torubber-like products of fluoroprene monomer or mixtures of fluoroprenewith other polymerizable materials in the presence of 0.5% to 5% of2,2-difluorobutene-3.

Fluoroprene, or a mixture of fluoroprene with other polymerlzableunsaturated compounds and 0.5% to 5% of 2,2-difluorobutene-3 (based onpolymerizable monomers), is dispersed in an aqueous system containing anemulsifying agent and a polymerization catalyst, preferably of thepersulfate or peroxide type. In most instances, it is preferable toinclude a sulfur containing modifying agent. The emulsion of monomers soobtained is polymerized at a temperature preferably in the range of 20to 40 C. The resulting latex, after being stabilized with an antioxidantsuch as phenyl-alpha-naphthylamine, is coagulated, and the rubber-likecoagulum is masticated and washed free of residual salts on a corrugatedrubber mill, and is finally dried by milling on a smooth rubber mill.The resulting coherent, plastic material is then compounded, molded, andvulcanized.

described in copending applications of Coflman and Salisbury Serial No.508,242, filed October 29, 1943, Salisbury Serial No. 508,243; nowPatent No. 2,426,792, filed October 29., 1943, and Barney Serial No.517,837, filed January 11, 1944. Consequently, it is advantageous to usea fluoroprene monomer from which the 2,2-difiuorobutene-3 has not beenremoved. Thus, the use of 2,2- difiuorobutene-3 not only aids inpreparing more plastic, readily processable fluoroprene polymers, but italso simplifies the purification of the monomer. It is preferable to usefluoroprene which is substantially free of monovinylacetylene andessentially free of peroxides.

The following examples are given to illustrate the invention. The partsused are by weight.

EXAMPLE 1 A mixture of 100 parts by weight of fluoroprene and 2 parts of2,2-difiuorobutene-3,

emulsified in 157 parts of an aqueous solution containing 4 parts ofsodium oleate, 0.5 part of excess sodium hydroxide, 1 part offormaldehyde/sodium naphthalenesulfonate condensation product, 1 part ofpotassium persulfate, and 0.1 part of potassium ferricyanide.Threetenths part of lauryl mercaptan is added, and the emulsion isheated for 5 /2 hours at 30 C. in a sealed glass-lined vessel equippedfor eflicient agitation. The resulting latex is treated with 2 parts ofa phenyl-alpha-naphthylaminediphenylamine (55:45) mixture dispersed inwater. The stabilized latex is coagulated by means of brine and aceticacid, masticated and washed free of residual salts on a corrugatedrubber mill, and finally dried on a smooth mill at an elevatedtemperature. The product consists of a coherent rubber-like materialwhich is more plastic and better milling than polyfiuoroprene preparedsimilarly except for the absence of 2,2- difluorobutene-Ii. The driedpolymer is compounded according to the following formula.

The. compounded stock is pressed to the desired shape in a mold andcured for minutes at 153 C. under pressure. .The vulcanlzate has awashed and dried as before.

tensile strength of 2610 p. s. i. at 310% elongation, and good oilresistance as indicated by a volume increase of only 76% after 2 days inkerosene at 100 C. The vulcanizate is further characterized by goodresilience, as indicated by Schopper rebound of 40%, and much bettersunlight and ozone resistance than natural rubber. Its freeze.resistance is particularly outstanding, as indicated by a Tm value-52 C.and T50=-41 C. The Tao test, used as a measure of freeze resistance, iscarried out as follows: A vulcanizate of uniform cross-section isstretched at least 170 and cooled slowly to 70 C. in this stretchedcondition. The tension on the sample is then released, the temperatureis raised slowly, and the sample is allowed to contract freely. Thetemperatures at which the sample shows and 50% of the total retractionpossible are the T10 and Tan value. respectively. Thus, the lower theT10 and Tan values, the greater is the freeze resistance.)

When fluoroprene is polymerized in the pres ence of smaller amounts of2.2-difluorobutene- 3, the improvement in plasticity, as to be expected,is somewhat less. A mixture containing 100 parts of fluoroprene and 0.1part of 2,2-difluorobu-tene-Zi, for example, when polymerized asdescribed above, gives a coherent, rubbery product which also has bettertack than polyfluoroprene prepared in the absence of the difluorobuteneand can be processed more readily on conventional rubber mills. Greaterimprovement in plasticity may be obtained by the use of larger amountsof 2,2-difluorobutene-3. With 5% of the latter, a plastic, coherentproduct is obtained in 97% yield which gives a vulcanizate showing atensile strength of 2980 lbs. per sq. in. at 380% elongation.

Exursu: 2

A mixture of 100 parts of fluoroprene and 2 parts of2,2-difluorobutene-3 is emulsified in 157 parts of an aqueous sodiumoleate solution as described in Example 1, but without the mercaptanmodifier. This emulsion is heated for six hours at 30 C. in a sealedglass-lined vessel. The resulting latex is stabilized with 2 parts ofantioxidant consisting of phenyl-alpha-naphthylamine/diphenylamine(55:45) added as a 50% dispersion in water. The latex is then coagulatedwith acetic acid and brine and the coagulum is The product consists of50 parts of a coherent rubbery material which is more plastic and easierto process than polyfiuoroprene prepared in the absence of thedifiuorobutene and a sulfur containing modifier.

Exams: 3

A mixture of 85 parts of fluoroprene, 15 parts of acrylonitrile, and 2parts of 2,2-difluorobutene- 3 is emulsified in 157 parts of an aqueoussolution containing 4 parts of sodium oleate, 0.5 part of sodiumhydroxide, 1 part of formaldehyde/sodium naphthalenesulfonatecondensation product and 1 part of potassium persulfate. One andone-quarter parts of lauryl mercaptan is added, and the emulsion isheated seven hours at 40 C. in a sealed glass-lined vessel equipped foretlicient agitation. The latex is stabilized and coagulated, asdescribed in Example 1. The coagulum is then washed and dried to obtaina quantitative yield of coherent rubbery material which mills betterthan a similar polymer prepared in the absence of 2,2-difluorobutene-3.

This rubber is compounded according to Formula I and vulcanized forthirty minutes at 141 C. to yield a tough elastic product havingexcellent oil resistance as indicated by only 27% volume increase aftertwo days immersion in kerosene at 100 C.

EXAMPLE 4 A mixture of 90 parts of fiuoroprene, 10 parts 01 styrene, and2 parts of 2,2-difiuorobutene-3 is emulsified in 157 parts of theaqueous solution described in Example 3. Three-tenths part or laurylmercaptan is added, and the emulsion is heated twelve hours at 40 C. Theresulting latex is stabilized and coagulated, and the coagulum is washedand dried to a quantitative yield of plastic, coherent rubber which canbe processed readily on conventional rubber equipment. Vulcanizates,prepared as described in Example 1, have a tensile strength of 3240 lbs.per sq: in. at 500% elongation and good rebound (42%). 1

It is to be understood that the examples are illustrative only, and thatany amount of 2,2-dlfluorobutene-3 within the limits of 0.05% to 5%,

based on the weight of polymerizables, can be employed. At least 0.05%of the 2,2-difiuorobutene-3 is required 'to obtain significantimprovements in mill behavior, and, if more than about 5% of the butenecompound is used, the

tensile strength of the resulting product may be impaired and thetackiness of the product may become excessive.

It is preferable in using fluoroprene prepared from monovinylacetyleneand hydrogen fluoride that the monomer be essentially free of peroxidesand acetylenic compounds, although attractive polymers from somewhatless pure fiuoroprene may be prepared by the proper adjustment of sulfurcontaining modifiers. Thus, if the fluoroprene contains an appreciableamount of monovinylacetylene, the use of an increased proportion of sucha modifier in the polymerization will tend to overcome the deleteriouseffects of the acetylenic compounds upon the properties of the rubber.While the examples illustrate only the preparation of improved polymersof 2-fluorobutadiene-L3, it is to be understood that the invention isapplicable likewise to polymerizable fluoroprene homologs such as2-fiuoro-3-methylbutadiene-1,3, 2-fluor0-3-ethylbutadiene-1,3, or2-fiuoro-3-propylbutadiene-1,3.

While the benefits derived from the use of difiuorcbutene are mostpronounced in polymerizations with fluoroprene itself, as illustrated inthe examples the invention is applicable to the preparation of improvedcopolymers of fluoroprene with other polymerizable organic compounds.Other polymerizable compounds which may be employed include styrene,acrylonitrile, vinylidene chloride, esters of acrylic and methacrylicacids, such as butyl acrylate and methyl methacrylate, vinylethinylcarbinols, e. g., dimethylwinylethinyll' carbinol, methyl vinyl ketone,butyl vinyl sulfone, vinyl pyridine, diisobutyl fumarate,N-n-butyl-maleic imide and 1,3-dienes, such as butadiene, lsoprene andchloroprene. The preferred polymerizable unsaturated compounds are thosewhich contain a terminal methylene group, as in the CH2=C group,because, in general, they copolymerize more readily with fluoroprene toproduce synthetic rubber-like materials having good oil and freezeresistance. Elastomers having greater oil resistance are obtained whenmonomer mixtures containing at least 25% and preferably more than 50% ofiluoroprene are employed. This invention can be used to preparesynthetic rubbar-like materials from mixtures containins more than twopolymerlzable monomers. such as mixtures of iiuoroprene, butadiene andacrylonitriie; iiuoroprene, butadiene and dimethyl (vinylethinyl)carbinol; and fluoroprene, dimethyl- (vinylethinyl) carbinol andacrylonitrile. To obtain multicomponent elastomers having improved oiland freeze resistance, the total diene content is preferably at least50%. of which at least 50% is fluoroprene.

The monomer mixture may be polymerized in any convenient manner. Goodresults are obtained by using the emulsion polymerization technique.Although the alkaline sodium oleate system, as described in theexamples, is generally preferred. other emulsifying agents may be usedin either alkaline or acid media with good results, such as the alkalisalts of naphthenic acids, long chain aliphatic sulfonic acids, orailryl naphthalene-sulfonic acids, etc. Betaines such as C-cetyl orN-hydroxy-propyl-C-cetyl-betaine and quaternary ammonium salts havinglong carbon chains, such as cetyltrimethyl-ammonium bromide, maylikewise be used. and combinations of emulsifying agents such as thealkali salts of oleic acid and resin may also be employed to advantage.It is possible to carry out the polymerizations under many diverseconditions and in the presence of many difl'erent ingredients commonlyused for the modification of haloprene it): butadiene hydrocarbonpolymerization sys- As the polymerization catalyst potassium persuliateis preferred, although other materials, such as hydrogen peroxide,benzoyl peroxide, or sodium perborate may be used if desired. Catalystactivators, such as potassium ferrlcyanide or sodium hydrosulfite usedin conjunction with persulfates or peroxides, are especially beneficialby way of accelerating polymerizations.

Polymerization modifiers, such as octyl. decyl, or lauryl mercaptans orcrude mixtures of long chain aliphatic mercaptans are preferablyemployed. However. other polymerization modifiers. such as sulfur,dialkyl xanthogen disulfides or carbon tetrachloride, may be used ifdesired.

6 such as aluminum sulfate, or by freezing, as described in U. 8, Patent2,187,146. The use of brine and an acid such as acetic or sulfuric acidis preferred for the coagulation of sodium oleate latices.

Processing of the coagulum can be carried out by cbnventional means.

The polymerization product prepared as described above may be compoundedin many different ways in order to obtain vulcanizates having differentproperties desired for specific uses. In general, the well-knowntechniques of compounding rubber and butadiene copolymer rubbers withsulfur, a vulcanization accelerator, and a metallic oxide, areapplicable to these products. The compounded mass may then be molded,sheeted. calendered, or, in general, formed to the desired shape andvulcanized. The vulcanization may be carried out at room temperature orabove, but

preferably between 130 C. and 170 C.

The products of this invention are especially valuable in applicationswhere materials which retain their rubber-like characteristics at' low.

temperatures, or incontact with oils or other chemicals, are required.Furthermore, they are particularly valuable for applications. whereozone and sunlight resistance are required in addition to oil and freezeresistance. Specific applications requiring one or more of theseproperties are encountered in certain automobile and airplane parts,such as carburetor or fuel pump diaphragms, gaskets, motor mounts,gasoline hose, airplane door seals, and the like.

I claim:

l. A synthetic rubber-like material of the .class consisting ofhomopolymers of a polymerizable 'il-fluoro-lfi-diene and copolymers ofthe .same with unsaturated compounds containing the terminal groupingCHs==C which are polymeriz-- able therewith in aqueous emulsions andfrom 40 monomer mixtures containing at least-50% of the Thepolymerization temperature may be varied alcohol, acids, and brine, orby heavy metal salts iI-fluoro-L3-diene, which polymers have beenobtained by emulsion polymerization of the mono-' more in the presenceof from 0.5% to 5.0% of 2,2-diiiuorobutene-3, based on the weight of thepolymerizabie monomers.

. 2. A synthetic rubber-like homopoiymer of iiuoroprene which has beenobtained by emulsion polymerization of the fiuoroprene in the presenceof from 0.5% to 5.0% of im-diiiuorobutene-li,

based on the weight of the fluoroprene.

WALTER E. MOCHEL.

REFERENCE! CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,950,481 Carothers et a]. nuMar. 13, 1034 2,000,080 Carothers' et al. Jan. ii. 198'!

